Introduction: Build a SpurtBot Line Follower

Picture of Build a SpurtBot Line Follower
NOTE:Before you decide to build this robot, please read my newer Instructable on building a SpurtBot Shadow Runner robot. The new design uses a solderless breadboard, so after you build the robot, you can experiment with your own circuits to control the robot in new ways. OK, carry on.

SPURT stands for School Projects Using Robot Technology, a concept introduced by the Rostock University, in Germany. You can find more about their program on their website at

These instructions are for building a very simple version of a line following robot, based on the SpurtBot design above. Thanks to Hartmut from Rostock University for his support in creating this design.

The schematic for the circuit is included in the images.

A version of these instructions can be found online at

You can also watch the video below for an explaination of how the SpurtBot works and a quick demonstration.

I hope you enjoy building your SpurtBot!


Step 1: Gather Your Materials

Picture of Gather Your Materials


• (2) Bearings from inline skates (Search YouTube for vids on how to remove and clean them.)
• (1) Balloon for Bands/tires (Use heavier duty 'punching balloon'.)
• (1) Popsicle/craft stick (I like nice color ones, but use whatever you like.)
• (1) 2 inch piece of 5/16 inch wooden dowel (The dowel should fit snugly into the bearings.)
• (2) Motors (3VDC, Jency Motor ST130-12240-38, Jenco part # 154915 or Mabuchi FK-260SA-10400, Jenco part # 2081908)
• (2) AA alkaline batteries
• (1) QRD-1114 reflective sensor
• (1) bc 337 NPN transistor
• (1) Resistor (50 to 100 ohm for IR emitter)
• (1) 10K ohm resistor (optional pull-down resistor may improve performance)
• (1) Battery holder for 2xAA batteries
• 8 inches of red wire
• 6 inches of white wire
• 6 inches of black wire


• Wire cutters
• Wire strippers
• Needle nose pliers
• Hot glue gun and glue sticks
• Soldering iron and solder
• Drill and 1/16 inch drill bit
• Sharp scissors
• Heat shrink tubing (1/16 inch, 3/32 inch, and 1/8 inch)
• Butane Lighter or other heat source

Step 2: Make Some Holes

Picture of Make Some Holes

Using the four leads of the QRD-1114 sensor as a guide, mark four dots near the very end of the craft stick.

Now use the three leads of the bc337 transistor to mark three dots about half an inch behind the dots for the QRD-1114.

The two sets of holes should be close enough to each other that the leads of the QRD-1114 when it is inserted can be bent back to make contact with the leads of the bc337 transistor.

Use a 1/16th inch drill bit to drill holes over each of the dots. Go slowly and be careful to avoid running the holes too close together. Use of a drill press is very helpful, but you can do it with a hand drill if you don’t have one. A wooden backer board underneath the craft stick will also help support the material while you are drilling.

When you are done, the craft stick should look a lot like the third picture.

Step 3: Attach the Dowel

Picture of Attach the Dowel

Mark the center of the dowel as a guide, and use the hot glue gun to attach the dowel on top of the craft stick. The dowel should be about 3/5th back from the front of the craft stick where the holes are drilled.

You want to be sure the dowel is square with the craft stick. I like to use the corner of a table to hold the two pieces of wood at 90 degrees while the hot glue is drying.


Step 4: Attach the Bearings

Picture of Attach the Bearings

Next place one bearing flat on its side. Hold the craft stick and dowel so that one end of the dowel is directly over the hole in the bearing. Being careful not to apply any pressure to the craft stick, push down firmly on the other end of the dowel until it is inserted fully into the bearing.

The end of the dowel should be flush with the surface of the side of the bearing, as shown in the 2nd picture.

Now repeat the process with the other bearing, so that you have one bearing on each side of the dowel. While you insert the second bearing, be careful to press down on the top of the dowel, rather than on the edges of the first bearing, or you might wind up with the dowel inserted too far into the first bearing.

Also be sure that the bearings are mounted at 90 degrees to the dowel. Congratulations, you now have a ‘rolling chassis’ for your SpurtBot.

Step 5: Attach Your Motors

Picture of Attach Your Motors

The motors need to be positioned carefully. Before you mount your motors, keep the following things in mind.

• The motor shafts need to be parallel to the rolling surface of the bearings. In other words, the motor shafts should be at 90 degrees to the craft stick and parallel to the dowel.
• The right motor shaft will need to be thickened with 3 to 4 pieces of heat shrink tubing. You need to leave about 1/8th of an inch between the shaft and the surface of the bearing to allow for the shrink tube to fit.
• Despite the above, you don’t want too much space between the motor shaft and the bearing, because it will add too much tension to the wheel when the bands are installed.
• To keep tension roughly equal on both bearings, you want both motors positioned the same distance from the bearings.
• The shaft of the right motor should be positioned directly behind the right bearing. The shaft of the left motor should be positioned directly in front of the left bearing.
• The shaft should overlap both sides of the bearing a little bit, so the tension bands will stay on the wheels.

OK, time to glue the motors on! Don’t sweat the points above too much. If you mess it up, hot glue is easy to remove and you can try again.

Start with the right motor, which will be mounted to the rear of the dowel. Position the motor and get a good feel for where it will go, noting the points above. Once you are ready, place a generous amount of hot glue on the craft stick and the dowel on the side the motor will touch.

CAUTION: Hot glue is, well… HOT. It will stick to your skin and burn you. The end of the hot glue gun is very hot. Don’t touch it, and don’t let it touch anything that can burn.

Pull the hot glue gun away quickly, and place it safely on the table. Working quickly, grab the right motor and place it on the SpurtBot.

You will have a few moments as the glue hardens, so check that the shaft is positioned as you want it. Then hold it still for a minute while the glue dries.

After the glue is dry, you can break off the little annoying threads of hot glue that inevitably happen.

Step 6: Mark You Connections

Picture of Mark You Connections

I like to mark all of my connections, so I don’t make (many) mistakes. Look at the SpurtBot from the top so that the front end with the holes is facing away from you.

Start with the four holes you drilled in Step 2 for the QRD-1114. Carefully mark the front-left hole with a ‘1’. Moving clockwise, the front-right hole is marked ‘2’. The hole just below that is marked ‘3’, and the hole just to the left of that is marked ‘4’.

Next, we’ll mark the three holes for the bc337 transistor. The left hole is marked ‘e’ for emitter. The center hole is marked ‘b’ for base. The right hole is marked ‘c’ for collector.

I also like to mark the shape of the bc337 transistor right on the SpurtBot, so I always insert it the right way. Make a little ‘D’ shaped marking behind the three mounting holes, with the flat side of the ‘D’ facing the front of the SpurtBot.

Step 7: Install the QRD-1114

Picture of Install the QRD-1114

Note: If the QRD-1114 sensor is inserted incorrectly, it will be destroyed as soon as power is applied, so take your time with this step.

The sensor will be mounted ‘dead bug’, meaning the sensor will be pointed down with its leads up in the air. Look at the QRD-1114 reflective sensor. There is one dark lens and one clear lens. Pin 1 of the sensor is marked with a dot on the top of the case by the dark lens. Many people have trouble seeing the dot, because it is very small. When mounted correctly underneath the SpurtBot, the clear lens will be towards the rear. See the picture below.

You will insert the leads up from the bottom, and through the four holes you drilled in the front of the SpurtBot in Step 2.

Make sure that lead 1 of the QRD-1114 is inserted into the hole you marked ‘1’.

Hold the QRD-1114 flush against the underside of the SpurtBot, and bend all four leads slightly outward to help hold the sensor in place.

Step 8: Install the Resistor

Picture of Install the Resistor

You are going to solder the resistor between pins 1 and three of the QRD-1114. A small 1/8th Watt resistor should fit nicely. Try to solder it so that it is as close to the craft stick as possible. This will help keep the QRD-1114 in place.

Solder one side of the resistor to pin 1 of the QRD-1114. It may be helpful to use an object to hold the other side of the resistor, or get a friend to help you. Don’t worry if the solder isn’t perfect.

Now go solder the other side of the resistor to pin 3 of the QRD-1114. Because the resistor is now held in place from your previous solder joint, this should be pretty easy.

If you need to, go back and re-solder the first side of the resistor, positioning it so that it is close to the surface of the craft stick, as mentioned above.

Check to be sure the QRD-1114 is still mounted flush to the underside of the craft stick. Adjust the two solder joints if needed to be sure the QRD-1114 is in place.

Cut off the leads from the QRD-1114 and the resistor at pin 3 only (refer to 2nd picture). Leave the leads of the QRD-1114 pin 1, 2 and 4 alone for now.

NOTE: I have found that adding a 10k ohm pull-down resistor between pin 1 of the QRD-1114 and ground improves performance.  It tends to make the line following more accurate in some situations by insuring the base of the BC337 transistor is pulled firmly to ground.

If you want to use the optional 10k ohm pull-down resistor, this would be a good time to install it. Solder the resistor across pin 2 and pin 4 of the QRD-1114, so that the 10k ohm resistor is sitting diagonally across the resistor you already installed between pin 1 and pin 3. Then cut the excess leads from the 10k ohm resistor, leaving the excess lead from the QRD-1114 pin 2 and pin 4 in place for now.

Step 9: Test Your Motors

Picture of Test Your Motors

You need to know which way your motors will turn when you connect power to them. So we are going to test them.

Insert the two AA batteries into the battery holder.

Start with the right motor, which is mounted behind the dowel with its shaft behind the right bearing.

Looked at from the right side, the bearing needs to turn clockwise for the SpurtBot to move forward. Since the motor will be attached to the bearing directly using a band, the right wheel motor also needs to turn clockwise.

Temporarily attach the black wire from the battery holder to one lead of the motor and the red lead from the battery holder to the other lead of the motor. Note which way it is spinning when viewed from the right side of the robot.

If it is spinning clockwise, mark the motor lead attached to the red wire with a ‘+’ and the motor lead attached to the black wire with a ‘-’.

If the motor is turning counter-clockwise, then you need to reverse the markings. Mark the motor lead attached to the red wire with a ‘-’, and mark the motor lead attached to the black wire with a ‘+’.

Now test the left motor. Repeat the above procedure, making sure the motor will turn counter-clockwise when viewed from the left side when you attach the battery leads.

Take your time with this step. As they say in carpentry, “Measure twice, cut once.”

Step 10: Connect the Red Wires

Picture of Connect the Red Wires

Preparation (refer to 1st picture)

Carefully strip about ¼ inch of insulation from one end of the red wire. Pinch the exposed conductors at the end of the wire between your thumb and forefinger, and twist the wire several times. This will help keep the individual conductors together while you work with them.

In the following steps, I will refer to this technique as ‘twisting the leads’. You’ll use this technique whenever you strip some insulation from the wire.

Next, use a clamp or other method to hold the exposed end of the red wire above your work surface, and tin the lead with your soldering iron. Use the smallest amount of solder you can. If you do not know how to tin your leads, look it up on the Internet or ask for help.

Now take the tinned end of the wire, and bend a little hook in it with the needle nose pliers.First Connection (refer to first picture)

First Connection (refer to 2nd picture)

 Wrap the hook of wire around pin 1 of the QRD-1114, and solder it in place. Be sure that the resistor is still soldered properly to pin 1 too.

You may now cut the extra leads of the resistor and QRD-1114 from pin 1 only . Leave the leads of the QRD-1114 pin 2 and 4 alone for now.

Second Connection (refer to 3rd picture)
Route the red wire back along the body of the SpurtBot toward the left motor. Avoid covering any of the holes or markings for the bc337 transistor.

Check the length you need to reach the ‘+’ lead of the left motor. Leave an extra ¼ inch and then cut the red wire. Strip about 1/8 inch from the end of the red wire, and ‘twist the leads’.

Insert the twisted end of the red wire through the left motor contact for the ‘+’ lead, but don’t solder it yet

Now take the remaining piece of red wire that you cut off earlier. Strip about 1/8 inch from the end and twist the leads.

Take the twisted end of this red wire and insert it into the same left motor ‘+’ lead as the other wire. It may be a tight fit. Get creative, but be sure you will have good electrical contact. Now solder both red wires to the left motor ‘+’ lead.

Check your solder joint carefully. Be sure both wires are firmly connected.

Third Connection (refer to 4th picture)

Now route the free end of the red wire between the two motors, towards the ‘+’ lead of the right motor. Once again, cut the wire about ¼ inch longer than the length needed to reach the contact. Then strip 1/8 inch from the end of the wire, and twist the leads.

Insert the twisted end of the red wire through the ‘+’ contact of the right motor, but don’t solder it yet.

Cut a 3 inch piece of red wire from what you have left. Strip both sides and twist the leads.

Now insert one end of this red wire into the same ‘+’ contact of the right motor, where you have already inserted the red wire coming from the left motor. Again, it may be a tight fit.

Solder both leads firmly in place.

Use your soldering iron to tin the end of the red wire. Then use the needle nose pliers to bend a hook in the end of the wire. 

Step 11: Install the Bc337 Transistor

Picture of Install the Bc337 Transistor

Insert Transistor (refer to 1st picture)

It’s time to install the transistor. Insert the transistor from the top of the SprutBot. Be sure to align the body of the transistors as it is marked. The flat side of the transistor should be facing the front of the SpurtBot.

The center pin should be in the hole marked ‘b’; this is the base of the transistor. The right pin should be in the hole marked ‘c’; this is the collector. The left pin should be in the hole marked ‘e’; this is the emitter.

Be sure to leave a little of the transistor leads showing at the top side of the SpurtBot. You will need to solder to the emitter lead from the top.

Connect Transistor Base (refer to 2nd picture)

Turn the SpurtBot upside down, and bend the left and right leads of the bc337 transistor outward. This will help keep the transistor in place. Leave the center lead of the transistor (the base) standing straight.

Now, take the lead from pin 2 of the QRD-1114 and wrap it underneath the SpurtBot. Use the needle nose pliers to carefully route the lead so that it touches the base (center pin) of the transistor. Keep the lead as close to the underside of the SpurtBot as you can.

Be very careful that the base lead and the QRD-1114 pin 2 lead only touch each other and nothing else.

Next, solder the QRD-1114 pin 2 to the base of the transistor. Double check that you have a good connection, and that those two leads are not touching anything else.

Then cut the extra lead off the base of the transistor. It is important that none of the leads from the transistor end up longer than the body of the QRD-1114, or they will drag when the SpurtBot drives.

Connect Transistor Emitter (refer to 3rd picture)

Turn the SpurtBot back over right side up. Bend the lead from the QRD-1114 pin 4 back along the body of the SpurtBot towards the emitter lead of the bc337 transistor. Use the needle nose pliers to position the QRD-1114 pin 4 lead against the emitter of the transistor.

Be very careful that the pin 4 lead of the QRD-1114 is touching the lead of the emitter and nothing else.

Carefully solder the pin 4 lead of the QRD-1114 to the emitter of the transistor. Double check that you have a good connection, and that those two leads are not touching anything else. It is easy to accidently short against the base of the transistor.

Trim the extra wire from the lead of the QRD-1114.

Step 12: Connect the White Wire

Picture of Connect the White Wire


Strip about ¼ inch from the end of the white wire. Twist the leads. Then tin the leads with your soldering iron using as little solder as possible.

Bend a little hook in the tinned end of the wire using the needle nose pliers.

First Connection (refer to 1st picture)

Now turn the SpurtBot upside down, and connect the hooked end of the white wire to the collector lead of the transistor. It is helpful to use the needle nose pliers to clamp the little hook shut onto the lead of the collector so it will stay in place while you work with it.

Be very careful that the white wire and the collector lead are not touching any other connections. 

Next, solder the white wire to the collector. Double check your connection.

Cut off the extra lead from the end of the collector.

Second Connection (refer to 2nd picture)

Now route the white wire along the underside of the SpurtBot, towards the right motor. The wire will cross the body of the SpurtBot to come up near the ‘-’ lead of the right motor.

Cut the white wire about ¼ inch past the length it needs to reach the ‘-’ contact of the right motor. Strip about 1/8 inch of insulation from the end of the white wire, and twist the leads.

Insert the stripped and twisted end of the white wire into the ‘-’ contact of the right motor and solder it in place.

Press the white wire against the underside of the SpurtBot so it is flush. Hold it in place with a dab or two of hot glue.

Step 13: Connect the Black Wire

Picture of Connect the Black Wire


Strip about 1/8 inch of insulation from the end of the black wire. Twist the leads. Tin the end with as little solder as possible.
Use the needle nose pliers to bend a little hook into the tinned end of the black wire.

First Connection (refer to 1st picture)

Now turn the SpurtBot upside down, and connect the hooked end of the black wire to the emitter lead of the transistor. It is helpful to use the needle nose pliers to clamp the little hook shut onto the lead of the emitter so it will stay in place while you work with it.

Be very careful that the black wire and the emitter lead are not touching any other connections. 

Next, solder the black wire to the emitter. Double check your connection.

Cut off the extra lead from the end of the emitter.

Second Connection (refer to 1st and 2nd pictures)

Now route the black wire along the underside of the SpurtBot, towards the left motor. The wire will cross the body of the SpurtBot to come up near the ‘-’ lead of the left motor.

Cut the black wire about ¼ inch past the length it needs to reach the ‘-’ contact of the left motor. Strip about 1/8 inch of insulation from the end of the black wire, and twist the leads.

Insert the stripped and twisted end of the black wire into the ‘-’ contact of the left motor, but don’t solder it yet.

Remove the batteries from the battery holder. Strip and twist the end of the wires if they are not already so prepared.

Insert the black lead from the battery holder into the same left motor ‘-’ contact as you previously inserted the black wire from the transistor emitter. Once again, this may be a tight fit.

Solder both black wires to the ‘-’ contact of the left motor. Be sure you have a good connection to both wires.

Press the black wire leading to the transistor emitter against the underside of the SpurtBot so it is flush. Hold it in place with a dab or two of hot glue.

Route the black wire leading to the battery holder between the two motors.

If the red lead of the battery holder is not already stripped, twisted and tinned, do so now. Use the needle nose pliers to put a little hook in the end of the wire. You will use this hook and the hook on the end of the other red wire to connect the battery to the SpurtBot.

Step 14: Quick Motor Test

We are getting close now. Time for a quick test to be sure we’ve got it all right so far.

Insert the two AA batteries into the motor case. Take the SpurtBot to a location with good lighting and have something with a bright white and dark black surface to test against.

Connect the hooked red wire from the battery holder to the hooked red wire coming from the ‘+’ contact of the right motor. The left motor should start to spin counter-clockwise when viewed from the left side of the SpurtBot.

Note that the wheels themselves will not spin, because we haven’t connected the traction bands yet. You can feel which way the motor is spinning by touching the shaft with your finger.

The right motor may not be spinning, which is fine. Place the SpurtBot on a bright white, well-lit surface. The right motor should now spin clockwise as viewed from the right side of the SpurtBot.

Place the SpurtBot on a black surface. The right motor should immediately stop spinning, while the left motor continues to spin.

If all works as described above, great! Move on to the next step.

If there’s a problem, check everything and test again.

Step 15: Attach the Battery Holder

Picture of Attach the Battery Holder

Now you can hot glue the battery holder to the top of the motors. Make sure to place the battery holder with the wires to the rear of the SpurtBot.

Place the battery holder as far forward as you can. This will keep the weight to the front of the SpurtBot, so the sensor maintains contact with the surface that it drives on. The battery holder should be balanced left to right along the central axis of the SpurtBot.

Step 16: Cut the Traction Bands

Picture of Cut the Traction Bands

Using a pair of sharp scissors, cut the ridged edge from the neck of the balloon.

Now cut two bands from the end of the neck, about the width of the bearings. Try to keep the cuts nice and straight.

You can fit the traction band onto the left bearing and motor shaft now. Start by stretching one band over the bearing on the opposite side from the motor shaft. Extend the band around the motor shaft.

Now carefully rotate the bearing. The band should tend to align itself onto the bearing and motor shaft.

Step 17: Thicken the Right Motor Shaft

Picture of Thicken the Right Motor Shaft

The right wheel needs to spin faster than the left when it is running. Because there is a small voltage drop across the transistor, the voltage applied to the right motor will always be a bit less than the left, which is connected directly to the battery.

However, by thickening the right motor’s shaft, we change the ratio of the diameters of the bearing and the shaft.

Effectively, you are changing the gear ratio. This will make the right motor spin faster. It will also have a little less torque, but it will be enough to move the SpurtBot, so that is OK.

Refer to the 1st picture. Find the smallest size shrink wrap tube you can fit over the right motor shaft. Measure a length that is just a tiny bit shorter than the length of the motor shaft, and cut the tubing with a pair of sharp scissors. Make your cut nice and square.

Place the cut tubing over the end of the right motor shaft.

Now you are going to use a lighter or other heat source to shrink the tubing. You should be very careful not to burn yourself, or to melt any parts of the Spurtbot.

Refer to the 2nd picture. Bend all wires out of the way. Think about where the flame of the lighter will go, and be careful not to melt the battery holder, bearing or anything except the shrink tubing.

Hold the SpurtBot in one hand, and apply the flame from the lighter briefly to the shrink tubing. It is better to apply the heat for a short time, and then go back a few times than it is to keep it on a long time.

Allow the shrink tubing to cool, then rotate the shaft 180 degrees and apply heat again. You should now have a nice tight fit.

Refer to the 3rd picture. Now find the smallest size shrink tubing that will fit over the last layer of tubing. Cut it to size and shrink it as before. You will need 3-4 layers of tubing. You may be able to use the same size tubing more than once, depending on how much it shrinks.

Check for the right size each time.

It is a good idea to test the SpurtBot once you have 3 layers of shrink tubing. You can always put another layer on later if you need it, but they are difficult to remove.

Refer to the 4th picture. Once you have 3 layers on the shaft of the motor and the shrink tubing is cool, you can install the traction band the same way you did for the left motor. Then got to the next step and test the SpurtBot. If it doesn’t turn right fast enough and stay close to the line, add another layer.

Step 18:

Picture of

Use a bright white surface with black electrical tape to make lines in a closed loop shape. You may need 2-3 widths of black tape to give your SpurtBot enough time to react to the sensor.

Start by testing inside the loop. Set the SpurtBot inside the circle so that it will move around the loop in a clockwise direction. When the sensor is on the black, the right motor will stop, and the SpurtBot will turn to the right. Now the sensor will cross over to the white background, and the right motor will spin faster than the left, turning the SpurtBot back towards the black line.

It should follow the line pretty closely, but may cut some tight corners.

Now place the SpurtBot on the outside edge of the black loop, facing so it will go around counter-clockwise. Once again, when the sensor is on the black, the right motor turns off and the SpurtBot begins to turn away from the loop. As soon as it hits the white background the right motor spins faster than the left, and the SpurtBot should turn back towards the line. If it follows the line pretty closely, all is well. If it doesn’t turn quite fast enough, try going back to Step 17 and adding one more layer of shrink tubing.

As you add layers, the right motor spins faster, but you are also reducing torque. If you add too many layers, the right motor may not have enough torque to move the SpurtBot.

Have fun!


superbotboy (author)2013-11-18

I found 'm28S VHAR' and it works pretty well.Thanks a ton for the recomendation and its a great instructable you've made so keep up the good work.Thanks again.

ignoblegnome (author)superbotboy2014-02-13

Thanks for sharing that info! I'm glad it worked out for you.

mraghib (author)2012-05-09

Sir one more question. What's a datasheet and how to study them? Sir i really need you help as i have just started to take an interest in robotics. Sorry for the too many quesyions i ask.

ignoblegnome (author)mraghib2012-05-09

If you are getting into robotics, then you will most definitely have to learn to research things on your own. If I feed you all the answers, you don't challenge yourself.

Here's your homework: Go find out what a datasheet is. Google can help you more quickly than I.

mraghib (author)ignoblegnome2012-05-10

A datasheet is a document summarizing the performance and other technical characteristics of a product, machine, component (e.g. an electronic component), material, a subsystem (e.g. a power supply) or software in sufficient detail to be used by a design engineer to integrate the component into a system.


ignoblegnome (author)mraghib2012-05-10

See? That was easy. I bet it was no more difficult to find the answer for yourself than it was to ask me. In fact, you get your answer quicker that way.

Now that you know what a datasheet is, hopefully you are already looking up the datasheets in question and studying them to learn what you need.

I'll even give you some advice. You will usually see something labeled 'Absolute Maximum Ratings' or similar. Don't design to those specifications. For example, if the maximum current rating of the IR LED in the CNY70 is 50mA, you want to operate it well below that.

Look lower down in the datasheet for more ratings that are more typical for normal operations.

One more hint, when you look at the pin diagrams for part, be sure you know if you are looking at the part from the top or from the bottom. That's an easy mistake to make.

mraghib (author)ignoblegnome2012-05-11

You told that i need to adjust the connection with the pins.
So for example- Pin 4 in QRD1114 is cathode, and pin 2 in CNY70 is cathode. So the connection that goes to pin 4 in this instructable which uses QRD1114 will go to pin 2 if i'm using CNY70.Am i right?

Here are some images:

ignoblegnome (author)mraghib2012-05-11

Thanks for posting this detail in your question. It will both makes your question clear and provides a reference for others in the future. Nice work.

And yes, you have it correct. Also, keep in mind the image on the right of the CNY70 is the bottom view, as though you are looking down at the pins.

mraghib (author)ignoblegnome2012-05-11

Thank You very much sir for your help. I've also subscribed to your posts on fb. Please make future instructables.

rimo (author)2012-05-08

sir i want to built this robot with cny70 please have a look but what kind of motors sould i choose im confused pliz reply siir

rimo (author)rimo2012-05-08

this is the link

ignoblegnome (author)rimo2012-05-09

This Instructable is based on the SpurtBot concept described on that university's web page, and one of the originators assisted me in adapting the design to my needs.

As I've said before, the CNY70 should work OK with this design (in fact I know it does). You just have to make some adjustments to the connections. Read through the other comments; there is some good info.

For the motors, if you cannot find the ones I specify, please read the notes on the picture in Step 1. If you hover your mouse over the motors, I provide some guidance on what to look for.

mraghib (author)2012-05-07

QRD1114 is not available to me,so can i use one of the following optical reflective sensors as a substitute:

RPR 220

Thank You

ignoblegnome (author)mraghib2012-05-08

Electrically, both the RPR 220 and TCRT-5000 look like good choices. I like the RPR 220 better, because it specifically states that it has a daylight filter on it, while the datasheet for the TCRT-5000 did not.

The problem both of these devices have is the detection distance. The RPR 220 needs 6mm, and the TCRT-5000 needs 12mm. Compare that to the CNY70, which needs 0.3mm (less than a mm).

Since the SpurtBot uses the detector as its front wheel/slider, the detection distance is critical.

If you want to try it, use the RPR 220, but add a small bead or other object to act as a front wheel. Be sure that the detector rests 6mm above the surface of the floor.

Let me know how it comes out!

rimo (author)2012-05-06

thnk you sir for reply
when i finished the robot i connect it to the battery just the left one turn and the right one never turn but when i use the 9v battery the 2 motors turn

ignoblegnome (author)rimo2012-05-08

It is possible that it didn't work with 2AA batteries because there was not enough current with the 75ohm resistor for the IR LED to light brightly enough.

However, with the 9V battery, I'm concerned you will burn out the CNY70 with too much current. Also, your robot will move much faster with 9V, so it will be harder to keep it on track.

I suggest you go back to 2AA batteries, but reduce the resistor to something like 58ohms. This will make the IR LED brighter by increasing the current for the same voltage. Make sure you use alkaline batteries, not rechargeables. Rechargeables only have about 1.2V each, which will not be enough. Of if your AA batteries were a little worn down, it might not work well. You

If you want to stick with a 9V battery, increase your resistor before you damage your CNY70. Look at the datasheet and you will see the maximum current is 50 mA, but you want to stay well below that. Typical voltage drop is 1.25V, but could be as high as 1.6V.

So let's say it is dropping the max voltage (best case), You subtract this from the battery voltage.

9V - 1.6V = 7.4V

So your resistor has 7.4V across it. Using Ohm's Law (I = V / R) , we can get the current through the resistor and IR LED.

Current (I) = 7.4V / 75 ohms = 0.0987 amps or 98.7 mA.
Way too high, even for the best case.

To pick your resistor, decide on your desired current. Let's try 35mA. Now rearrange the calculation to find the best resistor.

Resistance (R) = 7.4V / 0.035 A = 211.4 ohms. That's not a resistor value you can get, but you can get a 220 ohm resistor.

Remember I said this was 'best case'? If the IR LED only drops its typical 1.25V, will a 220 ohm resistor be safe? Let's see:

Current (I) = (9V - 1.25V) / 220 ohms = 0.03522, = 35.2 mA,
Still safe.

So in summary, either:
1) Go with two new alkaline AA batteries and reduce your resistor to 58 ohms. You could go a little lower. Use the calculations above to figure out how low is safe.
2) Try the 9V with a higher value resistor. 220 ohms should work well. Your robot will go faster so it may not work as well.

osh114 (author)2012-04-28

Do they sell these things in radio shack and can i use some small r/c motors?

ignoblegnome (author)osh1142012-04-28

They do not sell these anywhere. You have to buy the parts yourself.
I have a new instructable with a different version of the SpurtBot. I provide links where you can buy the components for that one.

If you hover over the picture in Step 1 of this Instructable, there are some notes on selecting the motors.

psrivastava (author)2011-10-13

thanx for the reply.i have one more question .reflective sensor that u have told about is not available in my it possible to use a combination of infrared LED and infrared phototransistor at the place of reflective sensor?
what will be the changes i would have to do in the circuit if i uses that combination.
please reply soon sir.

ignoblegnome (author)psrivastava2011-10-13

See if you can find the CNY70, which is another reflective sensor package that is similar to the QRD1114.

Alternately, you could use descrete infrared LED and phototransistors. The QRD1114 is just small versions of these components in a nice case. The case also provides some ambient light filtering.

So if you go with the descrete components, you may want to place a piece of shrink tubing over the phototransistor to help block some of the ambient light.

You would connect them just as shown in the schematic.

eltro (author)ignoblegnome2011-10-20

An extremely informative and interesting 'ible. The only problem i'm facing is that i'm not able to find either QRD1114 or CNY70 reflective sensor package.

As mentioned above,i understand that both QRD1114 & CNY70 packages contain a IR source & a two terminal Photo transistor(or Photo Diode maybe). So, it would be extremely helpful to me if you could mention the individual component number(e.g QRD1114 Reflective Sensor) of the combination of IR source & a two terminal Photo transistor that you say can replace the QRD1114 package.

ignoblegnome (author)eltro2011-10-20

The QRD and CNY packages are very nice because they not only hold the component in the correct position, they filter out interference from ambient light.

However, you can often find an IR emitter and detector sold as a pair. You may need to use some shrink tubing to enclose the detector and protect it from interference.

I don't have specific components to recommend, but see what you can find and use Ohm's Law and the values for the IR emitter forward voltage and the voltage of your supply (3V if you use two AA batteries as in this instructable) to calculate an appropriate current limiting resistor.

MegaDAS made it! (author)2017-04-28

A step by step guidance to make LINE FOLLOWER ROBOT, follow this project that provides Codes and circuits to make your own robot


Watch the complete project video from here:

ImNotRobot27 (author)2016-09-26

will it work out if i use 1 motor which spins both sides?

ImNotRobot27 (author)2016-08-24

Will QTR-8RC Reflectance Sensor Array work?

陳亮 (author)2015-11-10

Minimistic! Your wheel design is great!

ignoblegnome (author)陳亮2015-11-10

Thanks, but most of the credit goes to the folks at University of Rostock.

shufian (author)2015-05-26

sorry , sir

if i use ST 188 IR for sensor

how many ohm for the resistor ?

and what a kind transitor for i use?

thanks before

yhong4 (author)2015-05-24

Does it work with LRD and LED

ignoblegnome (author)yhong42015-05-24

I would not think so, no.

nrh3bat (author)2015-04-23

Can i make my own QRD 1114 sensor with IR LED and IR Phototransistor?

ignoblegnome (author)nrh3bat2015-04-24

You can, but it will lack the filters of a sensor like the QRD1114. So it won't work well in direct sunlight or anywhere there ours too much ambient IR light.

This post may give you an idea.

fahmy.p.ginanjar (author)2014-10-18

i can't found QRD-1114 and CNY-70 in my country. can i use LED and LDR ??

While you might be able to make your own sensor, I recommend you try to find an alternative part. Try searching for 'infrared reflective sensor'. The ST188 looks like it might work.

Good luck. Let me know if you find a working alternative, so others can benefit from your learning!

Rajat Rawat (author)2014-06-12

THANKS!!!! for the advice
But I don't know anything about robotics or how to adjust the circuit .Because I am in 8th class so i don;t want to risk trying anything and also the shop from which i get the sensors and transistors is very very far away and my uncle won't go again and again to bring the stuff.
So,if I attach a 9 volt battery will it work perfectly can the sensor or circuit be blown away .
I am avoiding the ball bearings of skate because it may cost me a fortune so I want to use the wheels instead I think It should work .
But I don't wan't to risk anything so please any more advices.

ignoblegnome (author)Rajat Rawat2014-06-13

You are changing the design significantly from this Instructable, so I cannot tell you it will be safe. In fact if you attach a 9V battery to this circuit, you will most certainly destroy the sensor. The design in this Instructable uses two AA batteries, which is 3V. If you us a 9V battery you will need to adjust the circuit.

Read through the other comments on this Instructable. I explain exactly how to determine the proper current limiting resistor using Ohms Law. It's really not too hard. Give it a try!

I'm willing to check your work and reply if you are willing to spend the time to read the comments, understand how Ohm's Law works, and calculate the resistor you need. I am not willing to just give you an answer with no work on your part, because you will learn nothing.

Do be careful with the sensors. As I've warned others in the comments, if you connect it without a properly sized resistor, you WILL damage it and it will be junk.

Make your calculations, I can check them, and THEN ask your uncle to get the parts you need. If the cost of the sensor is low enough, buy a backup. That way if you make a mistake you don't have to ask him to go to the store for you again.

Rajat Rawat (author)ignoblegnome2014-06-24

Thanks for all the help
I am gonna start it making in a few days

Rajat Rawat (author)ignoblegnome2014-06-16

I read the comment as you insisted me to but assume if I use a 100ohm transistor and a nine volt battery should it work and I have got another idea too why don't I use 3 AA alkaline batteries instead of 2 It should have enough current to move it in speed but still not enough to fry the circuit or make it tough to stay on the track.
Sir please reply my holidays are near end and I have to make the robot before it .

ignoblegnome (author)Rajat Rawat2014-06-16

I don't think you understand how to apply Ohm's Law. If you use a 100 ohm resistor (your comment said transistor, but I assume you meant resistor), and a 9V battery, you will destroy your sensor. What is the current that you expect to go through the emitter of the sensor with those values?
You could use 3 AA batteries, but again you need to apply Ohm's Law to find a resistor that will provide 20-30 mA through the emitter of the sensor.

Rajat Rawat (author)ignoblegnome2014-06-16

and Sir please tell me the names of sensors that I can use if QRD1114
is not available and please tell the names of those sensors in which I don't have to change the design or the circuit or anything so that I can just put the sensor instead of QRD1114 .
Thanks for the help sir
I will tell you as soon as I am able to make it

ignoblegnome (author)Rajat Rawat2014-06-16

There is a very similar part that some people have substituted, the CNY70. The pin placement is different on the two parts, so the connections need to be altered a little if you use the CNY70.
Read through the comments for details on how to use the CNY70 instead of the QRD1114.

Rajat Rawat (author)ignoblegnome2014-06-15

Thanks,that was a great help from your part I will certainly read other comments and if I don't understand them I will probably stick to the original design
Thanks a lot for the help

robobot3112 (author)2014-06-04

could i use 75 ohm resistor

ignoblegnome (author)robobot31122014-06-07

Based on your other comment, I'm assuming you are using the CNY70 instead of the QRD-1114. The short answer to your question is, "Yes, you can use a 75 ohm resistor."
A more instructive answer is this:

Search for and read the datasheet for the CNY70. Find the forward voltage of the emitter section of the CNY70. It is typically 1.25V, with a maximum of 1.6V

With two 1.5V batteries, you have a nominal voltage of 3V. Subtract the forward voltage drop of the emitter (3 - 1.25) and you get 1.75V remaining.

Using Ohm's Law is Current (I) = Voltage (V) / Resistance (R). To find the current in milliamps, you then multiply by 1000.

(1.75V / 75 ohms) * 1000 = 23.3 mA. That should be safe for current limiting the emitter in the CNY70. You want to stay well below the absolute maximum current rating of 50 mA, but high enough to ensure that the emitter puts out enough infrared light to be reflected and detected by the CNY70's detector.

robobot3112 (author)ignoblegnome2014-06-08

sir and whats more is that i dont find any effect of cny70 on the connected motor they move random

ignoblegnome (author)robobot31122014-06-10

Check over the expected behavior in step 18 and try to work out where you went wrong. One motor should be directly connected the battery; it should run forward continuously as long as you have the battery connected.

The other motor should only spin when there is an IR reflection detected on your sensor. If you lift the robot off the ground, that motor should stop. If it is on a nice white reflective surface, it should go. If it is on a black IR-absorbing surface, it should stop or slow down.

Other common issues:

The bot crossing the black line before the circuit has a chance to respond. In this case make your black line wider with multiple pieces of tape next to each other.

The controlled wheel not turning fast enough to follow the line. More layers of shrink tubing will help.

One or both motors hooked up backwards, causing the wheel to spin the wrong way. Go back and check your wiring.

Damaged sensor from accidentally running too much current through the emitter. It's pretty easy to do this; I've done it myself. If you run too much current through the emitter of the sensor by connecting power without an appropriately sized resistor, you destroy the sensor and just have to get a new one. You should be able to test to see if your sensor is responding at all.

Mis-connected circuit. Go back and check all of your connections.

robobot3112 (author)ignoblegnome2014-06-11

thanks . one last question sir how many volts should i power it with 68 ohms resistor

ignoblegnome (author)robobot31122014-06-11

I explained this in my previous reply about using Ohm's Law. Please review that answer.

You are essentially powering an IR LED inside the package of the CNY70 sensor. An LED is a specialized diode. Diodes drop a specific amount of voltage when you put a battery across them. This is called the forward voltage.

So when you connect an LED to a battery, it will drop the forward voltage. Without a current limiting resistor, too much current will flow through the LED and destroy it. To determine the size of the current limiting resistor, subtract the LED's forward voltage drop from the battery voltage, then use Ohm's law to select a resistor that will give you the current you want.

This should be 20-30 mA for this application. Higher current means the LED will light more brightly and you'll get a stronger reflection for the sensor. More is better, but stay well below the CNY70's absolute maximum rating of 50 mA.

robobot3112 (author)ignoblegnome2014-06-13

thank you very much sir and also for the speedy replies.

robobot3112 (author)ignoblegnome2014-06-08

thanks . but i saw the other comments and so i used 68 ohms it would work properly wont it

About This Instructable




Bio: I'm a robotics hobbyist and general tinkerer, among other things. Check out my blog or the LetsTalkRobots Playlist on YouTube: ...
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